1. Field of the Invention
This invention relates to the detection of materials deposited on the inner surface of a passage and, more particularly, a device and method for detecting mercury or other material deposits in a passage, such as a pipe through which hydrocarbon fluids are delivered.
2. Description of Related Art
Hydrocarbon fluids, such as crude oil, are often delivered through carbon steel pipes and other passages during and between operations for production, processing, storing, and the like. Some hydrocarbon fluids include mercury or other metals, which can be deposited onto the inner surface of the pipes as the hydrocarbon fluid passes therethrough. In some cases, a thin film of mercury or other materials can build up on the inner surface of the pipe. Such deposited mercury or other materials can present an environmental hazard and can be absorbed back into hydrocarbons passing through the pipe, such that even if a hydrocarbon fluid does not contain significant amounts of the mercury or other deposited material, the fluid can be contaminated by the mercury or other deposited material in the pipe.
When a pipe or other tubular passage becomes contaminated with mercury or other materials on its inner surface, a decontamination or cleaning operation is typically performed to remove the mercury or other materials. For example, the pipe can be drained of the hydrocarbon fluid and a cleaning fluid and/or a cleaning device can be passed through the pipe to remove the deposited mercury or other materials. Such cleaning operations can be performed at regular intervals or only when required. For example, mercury in the pipe can be detected in order to determine whether such a cleaning operation must be performed.
One conventional method for detecting mercury inside a pipe uses a strong source of x-ray radiation that can penetrate the pipe. The source of x-ray radiation is positioned near the pipe and directed toward the pipe so that the radiation passes through the pipe and impinges on a detection material, or x-ray film, on the opposite side of the pipe. The exposure of the detection material to the radiation is determined according to the type of the pipe as well as any mercury or other materials that are deposited inside the pipe. Thus, by examining the exposed detection material and identifying contrasting light and dark portions of the detection material, an operator can determine whether some portions of the pipe have internal deposits. For example, if liquid mercury has been deposited on a small spot on the inner surface of the pipe, the mercury will decrease the passage of x-rays so that the corresponding portion of the detection material (x-ray film) is less developed and is lighter than the surrounding areas. Thus, if the detection material includes a small, light spot that is lighter than the surrounding portions, the operator might conclude that the light spot represents an area of the pipe where the inner surface has a deposit of liquid mercury or other material. Similarly, mercury oxide and sulfide deposited on the inner surface of the pipe show up on the x-ray film as dark and white combinations that are different in contrast on the film than the pipe material.
While such an x-ray detection method has been used to determine local deposits of mercury and other materials, deposits can sometimes be difficult to detect using this conventional method. For example, if the pipe has a uniform film of mercury deposited on its inner surface, the operator may not detect any contrast between the different portions of the detection material and therefore may be unable to identify any deposit. Also, if other materials are deposited in the pipe, the other materials can also block the x-rays, such that the operator may be unable to determine what type of deposits have formed in the pipe. In addition, this conventional method typically requires safeguards to be taken to contain the strong x-ray radiation that is generated so that the radiation is not spread to equipment and/or people in the area.
Thus, a need exists for an improved method and device for detecting mercury and/or other materials that have been deposited on the inner surface of a pipe or other passage. The method should be capable of detecting deposits that are uniform over the inner surface, e.g., if the entire inside surface is coated with a film of material. Preferably, the method should be adapted to operate without the use of a strong x-ray machine and x-ray film.